Gas discharge lamps such as fluorescent lamps require a higher than normal operating voltage to be applied for starting so that the gas within the lamp ionizes. Traditionally, iron core and coil ballasts operating at a frequency of 50-60 Hz have been employed to generate the higher than normal operating voltage. Iron core and coil ballasts, however, are characterized by a poor power factor, heavy weight, and large physical size. Additionally, they generate harmonics, radiate an audible buzz, and produce a bothersome light flicker.
Solid-state high frequency electronic ballasts have been employed which use ferrite core transformers, improve the power factor, are smaller in size and less in weight, and produce virtually no audible noise. In these prior art ballasts, line voltage (50-60 Hz AC) is rectified to a DC voltage then inverted to an AC voltage by a power inverter to drive the lamp at a much higher frequency, typically in the range of 10-50 KHz.
In periods of peak electrical demand such as in the summer months, the utility companies have a difficult time meeting the needs of all their customers. One technique of sustaining service during peak demand is to "load-shed" non-essential loads. Another method is to reduce the service voltage, referred to as a "brownout". This typically involves lowering the nominal service voltage from 120 VAC to 115 VAC or slightly lower resulting in a 5%-10% savings in power. A limitation with the brownout technique is that some electrical equipment compensates for the lower voltage by drawing more current thus negating any advantage to the utility company. For example, the solid state ballast utilizes a switched mode power inverter having feedback for keeping the power constant. It will be appreciated that such solid state ballasts hinder the utility companies' attempt to shed loads.
Another limitation on the use of switched mode power inverter type ballasts is that they do not work properly with phase control dimmer switches, commonly used within incandescent lamps. This is so for the same reasons set forth above.